The enclosures for such switchgear are commonly of welded steel and are divided into compartments typically housing cables, current transformers, busbars, auxiliary equipment, and the circuit breaker.
With vertically isolatable switchgear--i.e. switchgear in which the circuit breaker is moved vertically within the enclosure to allow connection or isolation of the associated mains circuit--the circuit breaker is commonly located beneath the other compartments and typically includes a sealed chamber filled with insulating and arc interteruption media, for example SF.sub.6 gas.
Fault currents and voltages within the circuit breaker chamber may be extremely high and, if an abnormal condition should arise whereby the operational capability of the equipment is impaired, inadvertent and undesirable arcing may occur within the chamber.
The consequential temperature and pressure rises within the chamber resulting from this undesirable arcing may be so high that disruptive failure of the chamber can occur.
Although it is known to provide pressure relief means on the chambers to permit venting thereof once the pressure therein exceeds a predetermined value, the pressure created within the enclosure as a result of faults within the circuit breaker chamber can cause serious damage to the enclosure, particularly as this increased pressure is created in the lower regions of the enclosure and cannot be readily exhausted upwardly therefrom.
It would be desirable to be able to provide an enclosure for vertically isolatable electrical switchgear which is less prone to damage as a result of the effects of internal faults in the circuit breaker chamber.